Uranyl binitrate complexes have a particular interest in the nuclear industry, especially in the reprocessing of spent nuclear fuel. The modified PUREX extraction process is designed to extract U(VI) in the form of UO 2 (NO 3 ) 2 (L) 2 as it has been confirmed by EXAFS, XRD and TRLFS measurements. In this study, the L ligands are two molecules of N,N-di-(ethyl-2-hexyl)isobutyramide (DEHiBA) monoamide used to bind uranyl in its first coordination sphere. DEHiBA ligands can coordinate uranyl in

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... ther trans-or cis-positions with respect 1 to the nitrate ligands and these two conformers may co-exist in solution. In order to use luminescence spectroscopy as a speciation technique, it is important to determine whether or not these conformers can be discriminated by their spectroscopic properties. To answer this question, the spectra of trans-and cis-UO 2 (NO 3 ) 2 (DEiBA) 2 conformers were modeled with ab initio methods and compared to the experimental time-resolved luminescence spectra on the UO 2 (NO 3 ) 2 (DEHiBA) 2 systems. Moreover, the hydrated uranyl binitrate UO 2 (NO 3 ) 2 (H 2 O) 2 complexes in the same trans and cis configurations were modeled to quantify the impact of organic DEHiBA on the luminescence properties.